Kernel preemption leads to SATA instability (how to debug?)

Hi, I'm getting SATA instability on my system with kernel preemption
enabled. When accessing the SATA discs at the same time as other discs (for
example during a fsck of all file systems on the machine) it only takes a
few seconds for the SATA discs to start reporting things like this:

Interrupt storm detected on "irq20: atapci4"; throttling interrupt source
ad20: FAILURE - already active DMA on this device
ad20: setting up DMA failed

This is on a recent kernel (2004.07.18.05.00.00), but it's been like this
ever since the kernel preemption stuff was turned on again a few weeks ago.
With preemption disabled (by editing param.h) the system seems to be stable,
but somewhat sluggish (a simple bzip2 compress operation can generate a load
average of 10+).

How would I go about debugging this? Any hints would be appreciated. I do
have KDB/DDB and debug symbols compiled in, but the machine is a production
machine so I cannot afford long debugging sessions unfortunately.

Attached is the dmesg.boot and kernel config file. Below are some settings
that might be interesting from other files:

/etc/sysctl.conf
----------------
kern.ipc.maxsockbuf=524288
kern.ipc.somaxconn=1024
kern.maxfiles=16384
kern.polling.enable=1
kern.polling.idle_poll=0
kern.polling.burst_max=200
kern.polling.each_burst=25
kern.polling.poll_in_trap=1
net.inet.tcp.sendspace=262144
net.inet.tcp.recvspace=262144
net.inet.tcp.rfc3390=1
net.inet.tcp.inflight_enable=1
net.inet.tcp.inflight_min=6144
net.inet.tcp.inflight_debug=0
net.inet.tcp.sack.enable=1
net.inet.ip.intr_queue_maxlen=500

/boot/loader.conf
-----------------
kern.ipc.nmbclusters="16384"
hw.apic.mixed_mode=0
hw.intr_storm_threshold=5000

/etc/make.conf
--------------
CFLAGS= -O2 -pipe -fno-builtin
COPTFLAGS= -O2 -pipe -fno-builtin
CPUTYPE?=athlon-xp


/Daniel Eriksson